In the production process for electronic devices, upon patterning of electrodes and functional thin films, application of the technique for applying a material to intended separate regions utilizing a difference of the wettability with a liquid to the patterning of functional thin films has been proposed. This technique is a method in which a patterning layer having a region that is wettable with a liquid and another region that is unwettable with the liquid is formed on the surface of a substrate, then a liquid containing a material for forming a functional thin film is applied onto the patterning layer, and subsequently dried to form a functional thin film only on the region that is wettable with the liquid, to produce, for example, a wiring in an electronic device.
In order to prevent the liquid from spreading to a region other than the intended portion in carrying out printing using the image forming liquid used in the above-mentioned patterning of electrodes by various printing methods, such as ink-jet or screen printing, it is necessary to exclusively make the intended portion hydrophilic while keeping the surface of the region other than the intended portion hydrophobic.
In recent years, extensive studies have been made on the technique for applying a coating functional material to intended separate regions, by utilizing the finding that the contact angle of a polyimide film can be changed along with the change in the hydrophilic/hydrophobic property of the polyimide by appropriately selecting a polyimide precursor containing a hydrophobic side chain or a polyimide obtained from such a polyimide precursor as a patterning layer for electrodes, functional thin films or the like.
For example, the properties of a wettability changing layer obtained using a polyimide precursor or polyimide having an aliphatic ring are disclosed (see, for example, Patent Literature 1). The literature presumes that cleavage of the aliphatic ring of polyimide is one of the causes of changing the polyimide to be hydrophilic or hydrophobic. It also presumes that, as the amount of side chain (that is, the number of side chains) is increased, the surface energy (critical surface tension) of the polyimide is reduced, so that the polyimide becomes lyophobic.
Further, the examples of the literature show such results that, when a polyamic acid was obtained using an acid dianhydride having an aliphatic ring and a diamine having a hydrocarbon group in the side chain, and the polyamic acid was used in a wettability changing layer, irradiation of the layer with an ultraviolet light largely changed the hydrophilic/hydrophobic property of the layer. They further show that an electrode layer comprising PEDOT/PSS was formed on the wettability changing layer to produce an electronic device.